This actually turns out to be related to dd's default block size. By default, dd uses a block size of 512. The effect of this is that qemu fills the pipe buffer very quickly because dd just is submitting very small requests (that will require a RMW).
If you set an explict block size with dd (via bs=1M), you'll notice a significant improvement in throughput. So I think this turns out to be a libvirt issue, not a qemu issue. ** Changed in: qemu Status: Confirmed => Invalid -- virsh save is very slow https://bugs.launchpad.net/bugs/524447 You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs